This invention relates to the field of reactive ion etching and, more particularly, to a method for reducing the foreign matter deposited on a wafer during reactive ion etching.
In reactive ion etching, a radio frequency and static electric field are used to energize a gas which forms a plasma. The plasma is chemically reactive with the wafer and thereby induces etching. The reactive etch chamber is evacuated prior to the introduction of reactive gases and prior to applying a radio frequency ("RF") voltage within the chamber to form the plasma. The chamber is then evacuated to a particular operating pressure, generally between five millitorr and three hundred millitorr.
Reactive ion etching may also be supplemented with a magnetic enhancement. Typically, a mixture of reactive and non-reactive gases are flowed into the chamber and the RF voltage is applied therein. The magnetic flux may be imparted into the etching chamber, typically by means of electromagnetic coils, to direct charged ions in the plasma to particular locations of the etch chamber. This technique is often used to more precisely control the etching of the wafer. Reactive ion etching, both with and without magnetic enhancement, is a process which is well known in the art.
Preventing foreign matter from being deposited on the wafer during or immediately after the etching process has been a major concern in reactive ion etching. Generally, during etching, particles generated during the process become ionized and are suspended above the wafer surface within the chamber. At the end of the etching process, when the RF voltage is deactivated, the particles fall to the wafer surface and are deposited thereon. These particles pollute the wafer surface and create defects which impair the performance of the resultant integrated circuitry. Particularly in horizontal reactive ion etch chambers, where the wafer is placed in a horizontal plane within the chamber, relatively large amounts of foreign matter can fall directly on the wafer surface after the RF voltage is deactivated.
Various techniques have been developed to reduce the foreign matter deposited on the wafer as a result of reactive ion etching. U.S. Pat. No. 4,718,975 issued Jan. 12, 1988 describes a system for reducing particle contamination at the end of the etching process. In this technique, a shield is moved above the wafer to prevent falling particles from contacting the surface of the wafer. U.S. Pat. No. 4,761,199 issued Aug. 2, 1988 discloses a method where the reactive ion etch chamber contains a separate electrode having a potential applied thereto which attracts the charged foreign matter particles. The foreign matter is electrostatically attracted to the electrode and, therefore, will not fall on the wafer surface after etching is complete.
One drawback to these particular techniques is that they require an additional apparatus which must be implemented within the etch chamber. Therefore, to reduce foreign matter, the reactive ion etch chambers must be equipped with specially designed parts. Conventional reactive ion etch chambers have not been used, without modification, in a process for minimizing foreign matter deposition.
It is therefore an object of the present invention to provide a technique for reducing the foreign matter deposited on a wafer as a result of a reactive ion etching.
It is also an object of the present invention to provide a technique for reducing the foreign matter deposited on a wafer as a result of a reactive ion etching without the need for modifying a conventional reactive ion etch apparatus.
It is also an object of the present invention to provide a technique for reducing the foreign matter on a wafer produced using a reactive ion etch without impairing the etching process.